In my application I am having trouble with some false triggering of the PCA. In edge trigger (capture) mode the PCA sometimes fires on the wrong edge. It's significant, like 10% of the time.

Circuit details, opto-isolated pulsetrain input. Testing using Beckman signal generator. I can find no noise or improper signal levels on the port pin using the scope. If I put a .001 cap on the port pin the symptom goes away, but my max frequency is reduced. Interestingly, if I bypass the opto and put the generator right on the port, the symptom goes away. Is the edge "too sharp"?

Bizarre, huh?

Bob